This is a useful troubleshooting tool as it lets you know if your Internet connection is subject to Network Address Translation, which can make certain kinds of Voice over IP problematic.
You should compare this IP listed below with the IP address of the WAN port for your router. If they differ, your Internet connection is likely subject to additional Network Address Translation beyond your immediate control. This can cause problems with, among other things, the ability to make and/or receive calls using VoIP.
Your IP address is: